#!/usr/local/bin/perl
#!/usr/bin/perl
use 5.010;
use strict;
use warnings;
{
    package FlipFlop;
    use overload
      'bool' => \&fetch,
      '0+'   => \&numify,
      '""'   => \&numify
      ;
    sub new {
        my $class = shift;
        my $self  = !shift;
        bless \$self, $class;
    }
    sub fetch {
        my $self = shift;
        $$self = !$$self;
    }
    sub numify {
      shift->fetch + 0;
    }
}

my $fl = new FlipFlop;
say $fl;
say $fl;
say $fl;
say $fl;